Good section to look out for old consoles/computers for sale is at the DigitPress Buy/Sell forum section (<a href="http://digitpress.com/forum/forumdisplay.php?f=12">http://digitpress.com/forum/forumdisp lay.php?f=12</a>) Although you have to register to read it (and to contact the sellers) items pop up a lot there.
This person (<a href="http://digitpress.com/forum/showthread.php?t=118668&highlight=commodore">http://digitpress.com/forum/showthrea d.php?t=118668&highlight=commodor e</a>) claims to have a C64 for sale/trade. You're on your own otherwise but hope that helps you a bit.
toxicdog
Last time I saw one was in Dallas in a super mega pwn shop. Super rare now T.T
best bet would just be ebay but it does have its negatives...... good luck man.